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The strongest two-category combinations were commuter tax benefits teamed with facilities and amenities (6.8 percent VTR) and commuter tax benefits teamed with CWW (7.0 percent). The poorest results seem to come when on-site services are combined with rideshare matching (-3.2 percent VTR), non-financial incentives are paired with rideshare matching (-1.5 percent), and non-financial incentives are teamed with on-site services (-1.3 percent). Such seeming anom- alies often occur using models when complex modal tradeoffs are occurring in the calculations. In this particular test, however, a combination like rideshare matching with on-site services might be expected to lead to a more favorable result, given that the starting conditions are favor- able to ridesharing over transit. There are only eight cases in the 66 pairs pictured in Table 19-33 where the pairing actually results in a positive, or at least somewhat synergistic effect, i.e., the combination of the two strategies leads to a trip reduction impact that is larger than either strategy individually. These pairings are: commuter tax benefits teamed with CWW (7.0 percent VTR versus 5.0 percent and 3.8 percent individually) or with facilities and amenities (6.8 percent VTR versus 5.0 percent and 4.1 percent individually), CWW with facilities and amenities (5.7 percent versus 3.8 per- cent and 4.1 percent individually), parking management with facilities and amenities (4.2 per- cent VTR versus 3.0 percent and 4.1 percent individually) or with marketing (4.5 percent VTR versus 3.0 percent and 3.5 percent individually) or with financial incentives (4.8 percent VTR versus 3.0 percent and 4.1 percent individually), and financial incentives with facilities and amenities (4.9 percent VTR versus 4.1 percent and 4.1 percent individually) or with marketing (4.9 percent VTR versus 4.1 percent and 3.5 percent individually). In none of these scenarios is the synergy sufficient that the estimated trip reduction effect in combination is greater than the sum of the separately applied individual strategies. The Worksite Trip Reduction Model would appear to be an excellent start toward a set of tools that can help TDM planners make sense of the vast number of strategies available to them. In addition to being easy to use, a very appealing aspect of this new tool is that it does not seem to generate unrealistic estimates of trip reduction. The predicted reductions are generally on the order of 3 to 6 percent. Reduction estimates of this magnitude compare more realistically with the typical employment site results seen within large area-wide programs than do the 15 percent to 30 per- cent reductions seen in the 82-program sample. It should once again be stressed that the 82 exam- ples include many exemplary programs, and that that group should not in any way be construed as typical of what might be realized in a large area-wide regulatory program.14 Practitioners are urged to apply caution and common sense to any model projection, whether it be the two models featured in this subsection, or the FHWA TDM Evaluation Model, or the U.S. Environmental Protection Agency (EPA) COMMUTER Model introduced later in the "Additional Resources" section. Empirical case studies such as those presented in this chapter, or contained in a number of the recommended resources, always serve as a good way of cross-checking a TDM program's potential impact. International Experience Outside the United States, interest in TDM has been particularly high in the Netherlands and in the United Kingdom. A study prepared for the British Department for Transport (DfT), Smarter 14 During the timeframe of the Chapter 19 review and publication process, CUTR issued an update to the Worksite Trip Reduction model, now renamed TRIMMS (Concas and Winters, 2009). See the "Additional Resources" section for additional information. 19-119

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Choices--Changing the Way We Travel (Cairns et al., 2002), provides a summary of TDM experience in those two venues. Key studies and findings from the experience reviewed are summarized in the following section. Making Travel Plans Work15 This analysis and report was originally prepared for the DfT in 2002 by Cairns, Davis, Newson, and Swiderska of ESRC Transport Studies Unit UCL, and Adrian Davis Associates. It represented the biggest study of British workplace travel plans to date and presents results based on an analy- sis of best practice at 20 organizations employing over 69,000 employees. These cases represented a range of public and private organizations, all of which were selected as examples of good (not average) practice. Taken overall, the 20 organizations had reduced the number of cars driven to work by 14 for every 100 staff, representing an average reduction of 18 percent in the proportion of commute trips by car driver. On average, the organizations had doubled the proportion of staff commuting by bus, train, cycling, and walking, and car sharing (carpooling) had also been reason- ably successful. A study of factors that made some travel plans more successful than others produced very few generalizations that could be made. All travel plans had involved real changes to employee travel options, so it was not possible to assess the effects of plans that focused on awareness-raising only. The one factor that did emerge was parking. For the 13 travel plans that had addressed parking, either by restricting supply, introducing charges, or providing incentive payments to those giving up a parking space, the proportion of commute trips made as car driver was reduced by 24 per- cent, compared to 10 percent for those plans that had not addressed parking (Cairns et al., 2002). Effective TDM at Worksites in the Netherlands and the United States This study, performed by Organisational Coaching and Schreffler in 1996, compared 20 paired case studies from the Netherlands and the United States. The organizations examined included a large hospital, a large manufacturer, a government organization or utility, a bank, an insurance or telecommunications organization, a major university, an airport, a consultancy firm, and a smaller employer with less than 250 employees. Again, examples chosen were all considered to be success stories. Results showed remarkable similarity across the two sets of case studies, with the programs in the United States revealing VTR rates in a range of 6 percent to 49 percent, with an average of 19 percent, while those in the Netherlands had reductions in vehicle kilometers of travel ranging from 6 percent to 32 percent, averaging 20 percent (Cairns et al., 2002). Netherlands Ministry of Transport Study A 1998 Dutch study by Ligtermoet included a review of new results from 40 organizations in the Netherlands plus other Dutch data. Analysis showed that plans with "basic" measures (such as car-sharing schemes) achieved vehicle kilometer reductions of 6 to 8 percent, while those with "luxury" measures (such as company buses) or "push" measures (such as parking management) achieved reductions in the range of 15 to 20 percent. This led to the conclusion that plans combin- ing both "carrots and sticks" are the most effective (Cairns et al., 2002). 15 A "travel plan" is the equivalent of what is known in the United States as a Transportation Management Plan (TMP) (Enoch and Zhang, 2008). United Kingdom experience with travel plan employer participation rates is included in the "Site- Versus System-Level Impacts" subsection which follows. 19-120